"It's thrilling to hear her sing!" exclaims Rick Rubin. He's talking about Sugarland vocalist Jennifer Nettles, whose first solo album he's in the midst of producing. Rubin – who has worked closely with Red Hot Chili Peppers, Johnny Cash, Tom Petty and the Heartbreakers, Beastie Boys, Linkin Park, Adele and many others – clearly knows talent. And it seems the admiration is mutual on Nettles' end as well. "I'm super-respectful of his pedigree," says the country star of the famed producer. "I still get nervous around him, in a kind of a music-crush way."

Nettles' upcoming effort – as yet untitled, due out this fall – represents a number of firsts for her. It's her first major release outside the confines of Sugarland – one of country music's most beloved groups, bedecked with Grammys, CMT awards and platinum albums. "This album is different than what I've done before," she explains. "What I do with Sugarland, primarily it's stuff that starts with me and Kristian [Bush, Sugarland co-founder] writing together. It's fun to play with that masculine energy, but for this I wanted to do something really personal – more intimate and emotional."

For the new album, Nettles wrote songs on her own, or collaborated with top-shelf songwriters like Sara Bareilles and Butch Walker. It's her first musical project since giving birth to her four-month-old son, Magnus; according to Nettles, that pregnancy allowed her to take a crucial breather from the cycle of touring and recording. "I'm a working mother now," she says with a laugh before excusing herself to breastfeed her son. "The timing was right, both in the arc of my life and as an artist. You can get comfortable with certain sounds, and your fans come to expect them. At the same time, I wanted to play with different parts of my voice or my writing. It won't be a shock or surprise to a Sugarland fan, but hopefully it will bring in new listeners, too."

To get away from Sugarland's Atlanta and Nashville comfort zones, Nettles has holed up with Rubin for the past month in Shangri-La Studios, the Malibu, California site where classic sides from Bob Dylan, the Band, Eric Clapton, Jackson Browne, and many others were born. There, Rubin assembled a crack band of session pros, including Ian McLagan, ace keyboardist renowned for his work with Faces and the Rolling Stones; Red Hot Chili Peppers drummer Chad Smith; and bassist Jason Lader, who's played with Mars Volta. Virtuoso guitarists Smokey Hormel (who's played with Beck and Tom Waits) and indie-rock god Matt Sweeney (collaborator with Cat Power, Bonnie "Prince" Billy, and his own band Chavez) – both of whom contributed to Rubin's legendary comeback productions for Johnny Cash and Neil Diamond – were also on hand. "I put those people together to really get the sound of people playing in a room," Rubin says. "So much music today is done on a grid, played to a click track, perfectly in time. For Jennifer's album, we wanted a different, more intuitive and improvisational energy – we were searching for live inspirational moments."

"They're performances," Nettles says of the 20 or so songs she, Rubin and their team of players have come up with so far. "I love how human everything is. I've always wanted to capture the feeling of a live performance on a record, and this is as damn fine of an effort as I've ever done in that regard."

In an exclusive for Rolling Stone, Rubin previewed five tracks in progress. Close-miked acoustic guitars, funky grooves reminiscent of the Band and raucous honky-tonk piano flow through arrangements that Rubin calls "both ancient and modern." It's an ideal backdrop for Nettles' vocals, which in this context sound simultaneously more powerhouse and organic than she ever has on record before. "It goes in a lot of cool different directions," Rubin says. "There's country, but also blues, jazz, island rhythms, great classic rock moments, and a lot of soul. The organizing principle is Jennifer's voice and tastes. There's a lot of styles, but it all sounds like her."

Adds Nettles, "It's a celebration of my roots, and where I am today. I'm a different version of myself than what people might have known before – not only in my songwriting and performance, but even in the sounds on this album. It reflects a more soulful, grittier life. A lot has been lived in the time between the last record I made and now, and you can hear that."